Could be a wiring issue on the rfm module, Capacitor not close enough to radio, try changing between power levels, how far apart are radio modules? Try setting radio channel to 1 or 250 in order to move away from other possible interference.
In the previous experiments, I have put a big capacitor in the power source. The distance between node (ATMEGA328) and gateway (ESP8266 MQTT gateway) is less than 2 meter.
How to set the radio channel in RFM69 ?
Also how to set the power levels ?
Can you share the #define script of your working code, to see the pins configuration, channels or PA level ?